Clearance adjusting arrangement for an axial piston machine

ABSTRACT

A clearance is formed between the stationary control face of the valve plate and the rotary control face of the cylinder block of an axial piston pump or motor. Part-circular slots in the valve plate are located between two annular narrow sealing face portions which are subjected to great wear. Wide supporting face portions adjacent the narrow sealing face portions, are subjected to lesser wear which causes a high leakage flow. An abrading piston is biased by hydrostatic pressure, or by a spring, against one of the supporting face portions and increases its wear so that the clearance remains constant and leakage is reduced.

United States Patent 11 1 Kobald Apr. 2, 1974 [54] CLEARANCE ADJUSTING ARRANGEMENT 3,046,906 7/1962 Budzich 91/487 FOR AN AXIAL PISTON MACHINE 3,126,835 3/1964 Kline 91/487 3,267,871 8/1966 Lee ct al.. 91/485 Inventor! Waller Kvbald, 3,635,126 1 1972 Engel 91/487 Germany FOREIGN PATENTS OR APPLICATIONS 1 1 Assignccl g Bosch, GmbH, Stuttgart, 897,700 5/1962 Great Britain 91/485 crmany 22 Filed: Sep'" 11, 1972 Primary Examiner-William L. Frech Attorney, Agent, or FirmMichael S. Striker 21 Appl. No.2 287,994

[57] ABSTRACT 30] Foreign Application Priority Data A clearance is formed between the stationary control Sum 9 1971 Germany 2145058 face of the valve plate and the rotary control face of the cylinder block of an axial piston pump or motor. 52] us. c1. 91/487 Pan-circular slots in the Valve Plate are located 51 1 Int. Cl. F0lh 13/04 Ween two annular "arrow Scaling face Portions which 158 Field 0 Search 91/485-487 f subl'cted to great wcar- F Supporting F v tions ad acent the narrow scaling face portions, are [56] Referenc'es Cited subjectedto lesser wear which causes a high leakage UNITED STATES PATENTS flow. An abrading piston is biased by hydrostatic pressure, or by a spring, against one of the supporting face 2,241,701 5/1941 Doe 91/485 portions and increases its wear so that the clearance g ggs remains constant and leakage is reduced. 2:975:720 3 1961 Schoellhammer 91/485 12 Claims, 4 Drawing Figures 5-- v 7 7 ,IV/ 4 30 1 7 2s 1 1 N 1 l 1 BACKGROUND OF THE INVENTION The present invention relates to an axial piston machine in which the cylinder block containing the pistons rotates, and receives and discharges fluid through two part-circular control slots having on opposite sides narrow annular sealing face portions, on at least one side of which a wide annular supporting face portion is located. Axial piston pumps of this type have thedisadvantage that leakage losses cannot be kept low after prolonged use, if the pump is operated at high pressure, up to 300 atm. The pumped pressure fluid, such as oil, contains impurities which enter into the clearance or gap between the rotary control face of the cylinder block, and the stationary control face of the valve plate, and cause wear of the control faces which is greatest on the narrow sealing faces directly adjacent the semi-circular control slots. In the region of the annular comparatively wide supporting face portion which is adjacent the sealing face portions in the region of the greatest and/or smallest diameter where the cylinder block control face still is in contact with the valve plate control face, the wear is the smallest. A clearance or gap of different width results, which causes an increase of the leakage losses, which may cause malfunction of the pump. A pump of this type is disclosed in the German OS 2,034,391.

The US. Pat. No. 3,037,499, discloses an axial piston machine with a valve plate which is hydrostatically, and also by springs, pressed against the cylinder block. This axial pressure equalizes the forces occurring in the clearance between the control faces of the valve plate and of the cylinder block, which tend to increase the gap, and thereby prevent increase of the leakage losses. However, the one sided increase of, the width of the clearance caused by the wear of the annular sealing face portions, and the consequent leakage loss, cannot be prevented by the arrangement of the prior art.

SUMMARY OF THE INVENTION It is one object of the invention to provide a clearance adjuusting arrangement which brings about a uniform wear of the control faces'of the cylinder block and of the valve plate.

Another object of the invention is to reduce leakage losses by causing unifom'i wear of a stationary control face in sliding contact with a rotary control face.

With these objects in view, the present invention provides an abrading body in the region of the wide supporting face portions which slidingly engages one of the wide support face portions to cause the same to wear off to the same degree as occurs on the sealing face portions adjacent the control slots of the valve plate.

This has the advantage that by suitable arrangement of the abrading body, such a wear is produced on the wide supporting face portion that it corresponds to the wear of the narrow sealing face portion. The width of the clearance between the rotary and stationary control faces remains substantially constant, the leakage losses also remain low and constant, and the span of useful life of the axial piston pump is substantially increased.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING ing a modification of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1, la and 2, an axial piston machine has a housing 1, closed by a cover 2. A cylinder block 4 is secured to a drive shaft 3 for rotation therewith, and has axially extending cylinder bores 5 in which pistons 7 are mounted whose ends are provided with adjustable slide shoes 7a, sliding on the slanted surface-of a stationary wobble plate 6. A spring 8 abuts a ring 8a secured to cylinder block 4 and urges cylinder block 4 with its rotary control face 4a against the stationary control face 9 of a stationary valve plate 10 which is secured to housing 1. Housing 1 has inlet and outlet openings 11 and 12 which communicate with two part-circular slots 13 and 14 in valve plate 10 so that fluid flowing from inlet 11 through slot 13 is sucked into the ports of the cylinder bores 5 in cylinder block 4.

As best seen in FIG. 2, the part-circular slots 13 and 14 have ends separated by face portions, and are surrounded by narrow annular sealing face portions 15 and 16 which are, respectively, located radially outward, and radially inward of slots 13 and 14. An annular groove 17 surrounds the radially outer annular sealing face portion 16, and is connected by ducts 21, 22, 23 and 24 of which ducts 22 and 24 are shown in FIG. 1, with the interior of housing 1 for removing leakage flow from the clearance between thestationary and rotary control faces. A relatively wide annular supporting face portion 25 surrounds the annular groove 17 and the annular sealing face portion 16, and is in sliding contact with a corresponding annular wide supporting face portion of the rotary control face 4a of the cylinder block 4. Due to the fact that oil flowing through slots 13 and 14 contains impurities, the narrow sealing face portions 15 and 16 are substantially worn by the leakage flow into the annular groove 13. The wide supporting face portion 25 is subjected to lesser wear.

As shown in FIG. 1, the cylinder block 4 is provided in its control face 4a, with a stepped cylinder 26, 26 in which a stepped piston 27 is mounted, with play, for axial movement. A spring 28 in the end portion of cylinder 26 urges the piston 27, which at least partly con- I sist of an abrading material, against the wide supporting face portion 25 of the stationary control face 9 of valve plate 10. Abrading piston 27 has an annular shoulder 27 which forms with the shoulder 26' of the stepped cylinder bore 26, a small gap. A bore 29 passes longitudinally through the abrading piston 27 in order to reduce the pressure area on the front face of the abrading piston. Abrading piston 27 preferably consist, or at least is partly made of a sinter material with an abrasive component, or the abrading piston 27 may be covered with an abrasive coating.

During operation of the axial piston machine, a clearance or gap'develops between the stationary control face 9 of the valve plate and the rotary control face 4a of cylinder block 4 through which pressure fluid flows from the control slots l3, 14, particularly through the slot which is subjected to high pressure into the inner cavity of housing 1. Part of the leakage flow flows through a duct 30 into the cylinder bore 26. As shown in FIG. 1a, the end of the duct is located on the control face 4a in the region of a narrow sealing face portion 16. Due to the very substantial play between the abrading piston 27 and the cylinder 26, no pressure develops in the end chamber of cylinder 26, and the play is selected so that the amount of pressure fluid which at the correct width of the gap between the control faces 9 and 4a, enters cylinder 26, can flow freely through the gap between the shoulder 27' of the abrading piston 27 and the shoulder 26" of the stepped cylinder 26, 26 into the inner cavity of the housing 1.

The pressure spring 28 is weak, and so dimensioned that the abrading body 27 is held in contact with the supporting face portion 25 of the stationary control face 9, but does not cause substantial wear during sliding of abrading piston 27 on the supporting face portion 25.

If due to wear in the region of the sealing face portions 15, 16, the width of the clearance between the rotary control face 4 of the cylinder block and the stationary control face 9 of the valve plate, is increased, a greater volume of fluid enters cylinder 26 under higher pressure so that pressure is developed in cylinder 26, irrespective of the leakage flow into the interior of housing 1, so that the abrading piston is pressed in axial direction against the supporting control face portion 25 of the stationary control face 9. 1

Due to the increased pressure and also due to the im purities contained in the pressure fluid which enter through the longitudinal bore 29 in abrading piston 27 between the end face of the abrading piston 27 and the supporting face portion 25, wear on the supporting control face portion 25 is increased. When the supporting face portion 25 is worn, the rotary control face 4a of cylinder block 4 can move closer to the control face 9, so that the width of the gap or clearance in the region of the sealing face portions and 16 is reduced. This automatic adjustment is continued until the wear of the sealing face portions 15, 16, and of the supporting face portion 25, is substantially equal, and the width of the gap between the control faces 9 and 4a is substantially constant within the entire gap, and so small that the leakage losses do not exceed a permissible maximum. In this operative condition of the radial piston pump, the pressure of the pressure fluid in the cylinder bore 26 is again reduced, so that the abrading body 27 is held only by the small force of spring 28 in contact with the supporting face portion of the control face 9 of valve plate 10.

FIG. 3 illustrates a modified embodiment in which the abrading piston and cylinder are not provided in the cylinder block, but in the valve plate.

Referring now to FIG. 3, a cylinder block has a rotary control face 35a slidingly abutting the stationary control face 36 of a valve plate 37. The stationary control face 36 has, on opposite sides of the control slot means 38, narrow sealing face portions 39, 14. Grooves 41 and 42 for receiving the leakage flow from the control slots 38 are provided adjacent the narrow sealing face portions. Channels 43, 44 connect the grooves 41, 42 with the interior of housing 1. Adjacent the grooves 41, 42, an inner supporting face portion 45 and an outer supporting face portion 46 are provided. The valve plate 37 has, in the region of the slot 38 associated with high pressure fluid, a stepped cylinder 47, 47 in the outer supporting face portion 46, in which an abrading piston 48 is mounted, guided in the cylinder portion 47 with ample play, and biased by a spring 49 with a small force against the cylinder block 35. In the inner supporting face portion 45, a stepped cylinder 50, is formed in which the abrading piston 51 is mounted with play in the cylinder portion 50. A spring 52 urges the abrading piston 51 with a small force against the corresponding face portion of the rotary control face 35a of the cylinder block 35. A duct 53 open in the region of the outer sealing face portion 40, ends in the stepped cylinder 37, while a duct 54 open at the inner sealing face portion 39, communicates with the stepped cylinder 50.

The abrading bodies 48, 51 have on the front face abutting the control face 35a a diameter which corresponds to the radial width of the wide annular face portions 45 and 46. Abrading piston 48 has a central longitudinal bore 55, and abrading piston 51 has a similar bore 56.

The operation of the embodiment of FIG. 3 takes place as described above, with reference to the embodiment of FIG. 1. However, wear takes place on the rotary control face 35a of the rotary cylinder block 35, instead of on the stationary control face of the valve plate 37. The stationary control face is also subjected to wear, so that after prolonged use of the machine, corresponding contours of the control faces are formed, which remain at a constant distance from each other so that the leakage losses remain constant.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of clearance adjusting arrangements for axial piston pumps, differing from the types described above.

While the invention has been illustrated and described as embodied in an axial piston pump provided with a biased abrading piston in contact with little worn face portions of the control face of a valve plate for maintaining a constant clearance and leakage flow between the control face of the valve plate and the rotary control face of the cylinder block of the machine, it is not intended to belimited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

I claim:

1. Clearance adjusting arrangement for'an axial piston machine, comprising a housing having an inlet and an outlet; cylinder block means mounted in said housing forrotation about an axis and having a rotary control face formed with cylinder ports; valve plate means secured in said housing and having two part-circular control slots communicating with said inlet and outlet, respectively, and being swept by said cylinder ports, said valve plate means having a stationary control face in sliding contact with said rotary control face, and including two narrow annular sealing face portions radially inward and outward, respectively, of said control slots, and at least one wide supporting face portion radially adjacent one of said sealing face portions and in sliding contact with a supporting face portion of said rotary control face so that impurities in the fluid leaking from said slots cause greater wear of said narrow sealing face portions than of said supporting face portions, at least one of said means being formed with a cylinder in the region of the respective supporting face portion, and including an abrading piston in said cylinder biassed into engagement with the supporting face portion of the control face of the respective other means for causing wear thereof corresponding to the wear of said narrow sealing face portions so that the clearance between said control faces remains constant and small whereby leakage losses are reduced.

2. Arrangement as claimed in claim 1 and including spring means in said cylinder for urging said abrading piston into engagement with said supporting face portion of the control face of the respective other means.

3. Arrangement as claimed in claim 1 wherein said abrading piston has a diameter smaller than the diameter of said cylinder so that said abrading piston has play in said cylinder.

4. Arrangement as claimed in claim 1 wherein said cylinder is formed at least in said supporting face portion of said stationary control face of said valve plate means; and wherein said valve plate means includes a duct connecting a pressure area with said cylinder so that said abrading piston is biased by hydrostatic pressure.

5. Arrangement as claimed in claim 1 wherein said cylinder is stepped and has a portion of small diameter connected by an annular shoulder with a portion of large diameter; and wherein said abrading piston is a stepped piston fitting with play in said cylinder; spring means in said cylinder; and a duct in said one means connecting a pressure area with said cylinder.

6. Arrangement as claimed in claim 1 wherein said abrading piston is at least partly made of a sinter metal.

7. Arrangement as claimed in claim 1 wherein said abrading piston is made of a base material coated with an abrading coating.

8. Arrangement as claimed in claim 1 wherein part of said abrading piston is made of an abrasive material.

9. Arrangement as claimed in claim 1 wherein said cylinder is formed in said cylinder block means, said cylinder block means including a duct connecting a pressure area with said cylinder so that said abrading piston is hydrostatically pressed against said supporting face portion of said stationary control face of said valve plate means.

l0. Arrangement as claimed in claim 1 wherein said cylinder is formed in said valve plate means, said valve plate means including a duct connecting a pressure area with said cylinder so that said abrading piston is hydrostatically pressed against said supporting face portion of said cylinder block means.

ll. Arrangement as claimed in claim 1 wherein said one means is formed with a duct connecting the control face of said one means with said axial cylinder so that leakage flow through said clearance hydrostatically presses said abrading piston against said supporting face portion of the respective other means.

12. Arrangement as claimed in claim 11 wherein said duct has one end opening in the clearance between one of said sealing face portions and the corresponding face portion of the respective other means. 

1. Clearance adjusting arrangement for an axial piston machine, comprising a housing having an inlet and an outlet; cylinder block means mounted in said housing for rotation about an axis and having a rotary control face formed with cylinder ports; valve plate means secured in said housing and having two partcircular control slots communicating with said inlet and outlet, respectively, and being swept by said cylinder ports, said valve plate means having a stationary control face in sliding contact with said rotary control face, and including two narrow annular sealing face portions radially inward and outward, respectively, of said control slots, and at least one wide supporting face portion radially adjacent one of said sealing face portions and in sliding contact with a supporting face portion of said rotary control face so that impurities in the fluid leaking from said slots cause greater wear of said narrow sealing face portions tHan of said supporting face portions, at least one of said means being formed with a cylinder in the region of the respective supporting face portion, and including an abrading piston in said cylinder biassed into engagement with the supporting face portion of the control face of the respective other means for causing wear thereof corresponding to the wear of said narrow sealing face portions so that the clearance between said control faces remains constant and small whereby leakage losses are reduced.
 2. Arrangement as claimed in claim 1 and including spring means in said cylinder for urging said abrading piston into engagement with said supporting face portion of the control face of the respective other means.
 3. Arrangement as claimed in claim 1 wherein said abrading piston has a diameter smaller than the diameter of said cylinder so that said abrading piston has play in said cylinder.
 4. Arrangement as claimed in claim 1 wherein said cylinder is formed at least in said supporting face portion of said stationary control face of said valve plate means; and wherein said valve plate means includes a duct connecting a pressure area with said cylinder so that said abrading piston is biased by hydrostatic pressure.
 5. Arrangement as claimed in claim 1 wherein said cylinder is stepped and has a portion of small diameter connected by an annular shoulder with a portion of large diameter; and wherein said abrading piston is a stepped piston fitting with play in said cylinder; spring means in said cylinder; and a duct in said one means connecting a pressure area with said cylinder.
 6. Arrangement as claimed in claim 1 wherein said abrading piston is at least partly made of a sinter metal.
 7. Arrangement as claimed in claim 1 wherein said abrading piston is made of a base material coated with an abrading coating.
 8. Arrangement as claimed in claim 1 wherein part of said abrading piston is made of an abrasive material.
 9. Arrangement as claimed in claim 1 wherein said cylinder is formed in said cylinder block means, said cylinder block means including a duct connecting a pressure area with said cylinder so that said abrading piston is hydrostatically pressed against said supporting face portion of said stationary control face of said valve plate means.
 10. Arrangement as claimed in claim 1 wherein said cylinder is formed in said valve plate means, said valve plate means including a duct connecting a pressure area with said cylinder so that said abrading piston is hydrostatically pressed against said supporting face portion of said cylinder block means.
 11. Arrangement as claimed in claim 1 wherein said one means is formed with a duct connecting the control face of said one means with said axial cylinder so that leakage flow through said clearance hydrostatically presses said abrading piston against said supporting face portion of the respective other means.
 12. Arrangement as claimed in claim 11 wherein said duct has one end opening in the clearance between one of said sealing face portions and the corresponding face portion of the respective other means. 